What life is


Evidence of Evolution

Let's have a look at the type of evidence that supports Darwin's theory of evolution and the modern synthesis, which combines natural selection with the concept of species and population genetics. The latter is the modern application of the patterns of inheritance as first described by Gregor Mendel (1822-1884), a contemporary of Charles Darwin (1809 -1882).

Evidence of evolution comes from categorizing similarities among organisms living on distant locations, e.g., continents. Biogeography was central to Darwin's logic when he summarized his findings from five years of collecting evidence around the world as a passenger on the HMS Beagle. He realized that animal and plant species, though diverse, were more similar to each other on the same continent. Australian species were more similar to each other than they were to South American species. But such geographic diversity also played out on local island groups such as those of the Archipelago Galapagos in the South Pacific. The famous Darwin finches were his prime exhibit in formulating the theory of evolution. The idea is that species change over time in different direction if they live isolated from each other over long periods of time. Time periods in evolution are truly long and are measured in geological time, e.g. MYA or million years ago.

Fossil records together with the theory on plate tectonics and continental drift support the idea of speciation as a result of long lasting geographic isolation. Speciation is the process of evolving two separate species from a founder species after an event caused separation of the founder population into two isolated population where individuals from one population cease to reproduce with individuals from the other population.

Evidence of diversity and similarity comes from comparative anatomy and comparative embryology. Often, we find similar anatomical features in animals and plants that are used for different functions. Examples are the human arm used for grabbing, whose skeletal anatomy looks similar to that of the forelimb of a cat used for walking, but also looks similar to the skeletal anatomy of the flipper of a whale used for swimming and the wing of a bat, used for flying. The bone structures in all four limbs are strikingly similar in their anatomical plan, suggesting that the four different animals are all descendants of a common ancestral animal form. Each modern animal has evolved independently of all others and has adapted a limb structure that fits the different usage. They have, however, not changed completely and are considered homologous structures. The idea of homology points towards a structural similarity of body parts that are used for different functions. In some instances, organisms that are clearly not related have evolved similar structures for the same function. This structural similarity for the sake of the same function is the result of convergent evolution. Such structures are called analogous, indicating that their similarity, unlike the structural similarities of homologous structures, is not the result of descent with modifications.

Some of the most convincing evidence comes from modern molecular biology demonstrating that similarities at the molecular level - protein structures and gene sequences - can be used to determine evolutionary relationship. Molecular evidence has spectacularly supported the theory of evolution The power of molecular analysis is straight forward; the modifications mentioned by Darwin are really the result of random mutations in our genes. Genes contain the instructions to make proteins. Proteins are the true causes of physical traits. It is these traits that are edited by natural selection, i.e., how well an individual organism can live in changing environments and has the opportunity to have as much offspring as possible. It is the number of fertile offspring that is the true measure of Darwinian fitness. It is not, as many people believe, the survival of the fittest, often meant to mean the strongest individual. The meaning of strength is relative and is often shaped by chance events. As a result, descent with modification is neither directed nor is it able to create the perfect species. Perfection often means reduced ability to adapt, to make use of modifications when the environment changes drastically. Drastic changes are thought to be global climate changes such as warming and cooling. Most organisms are very sensitive to the average temperature, or their food, i.e., the organisms they feed on may be very sensitive to changes in temperature and disappear, leaving even the strongest of animals in limbo, without food, and thus may risk extinction if it cannot change its way of life.

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